1. Field of the Invention
The present invention relates to a heating apparatus which heats a substrate in a vacuum quickly, a heating method which employs the heating apparatus, and a semiconductor device manufacturing method employing the heating method.
2. Description of the Related Art
A semiconductor manufacturing technique frequently requires a process for heating a semiconductor substrate quickly. In particular, activation annealing of a wide bandgap semiconductor represented by silicon carbide (SiC) requires a high temperature of approximately 2,000° C. Regarding this, a substrate heating apparatus employing electron impact heating is known in which thermoelectrons are extracted from a filament upon application of an acceleration voltage between the filament and a vacuum vessel, and caused to collide against a heater, thus generating heat (see Japanese Patent Nos. 2912613, 2912616, and 2912913).
FIG. 3 is a view showing the structure of a vacuum heating vessel employing electron impact heating in a conventional heating apparatus.
Referring to FIG. 3, a 120-mm diameter conductive heater 1310 made of graphite (carbon) is present in the upper portion of a vacuum heating vessel 1030 to form one surface of the vacuum heating vessel 1030. In the vacuum heating vessel 1030, a filament 1320 made of tungsten-rhenium is fixed to a base plate 1340 made of molybdenum through tantalum first support columns (filament support columns) 1330. The base plate 1340 is fixed to an intermediate base plate 1370 made of molybdenum through second support columns 1360. Three heat reflecting plates 1350 made of molybdenum are inserted in a direction opposite to the filament 1320. The intermediate base plate 1370 is fixed to a water-cooled flange 1400 through third support columns 1390. Insulation glass members 1380 are arranged on and under the intermediate base plate 1370.
In the conventional heating apparatus, the emissivity of the heat reflecting plates 1350 can be decreased, so heat insulation can be achieved easily, thus improving the heating efficiency. When temperature of the conductive heater is in a high-temperature range, that is, at 2,000° C., the temperature difference between the upper and lower surfaces of the base plate located closest to the filament is large. Hence, the base plate which fixes the columns that support the filament warps to project toward the conductive heater. The support columns accordingly spread outward and apply an excessive force to the filament, thus bending the filament.
In this manner, if an excessive force acts on the filament to bend it, short-circuiting may occur to generate abnormal electric discharge. Also, the electron emission distribution becomes nonuniform and degrades the uniformity of the substrate surface temperature.
Also, when the temperature of the molybdenum base is 1,800° C. or more, sublimated molybdenum may be attached to the insulating glass members, which causes an insulation error soon.